JP2866653B2 - Surge arrester - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surge arrester for high voltage. The surge arrester includes a working portion including a plurality of substantially cylindrical surge arrester elements of metal oxide varistor material disposed coaxially between two end fittings, and an end portion. A support portion with at least one rod of insulating material extending between the fixtures to mechanically hold the surge arrester together. This surge arrester is mainly used for voltages of the order of 100 KV or more, but in principle the same embodiment can be used for lower voltages.

BACKGROUND OF THE INVENTION Surge arresters of the type described above are disclosed in U.S. Pat.
It has already been known since 2,318. In this known surge arrester, a plurality of surge arrester elements in the form of zinc oxide varistors are stacked and housed in a porcelain housing. As the surge arrester element is housed in the housing, a gap is formed between the housing and the varistor stack. If a problem occurs inside the surge arrester and a short-circuit current occurs or ultraviolet gas is generated, a large pressure will be applied to the above-mentioned gap. Therefore, such structures require the use of special and expensive means to relieve pressure, to prevent fires in the housing, to prevent disassembly, and to avoid secondary disasters. Other disadvantages associated with this structure include the relatively large space requirements and the limited number of varistors stacked in the same porcelain housing.

Surge arresters, in which the arrester element comprises a tightly surrounding housing made of a shrinkable plastic or rubber material, are already known (GB-A-2 073 965). As a method of mechanically reinforcing the surge arrester, it has been proposed to arrange an insulating rod between end fittings of the surge arrester. This rod is a surge arrestor
It extends through an axial hole in the element. However, such a structure presupposes the use of an airtight housing that shields the rod from the external environment. Unless such a shielding structure is adopted, there is a risk that a creep current is generated. This creep current may cause a flashover in the gap that is necessarily created between the rod and the wall of the hole.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surge arrester configured for high voltage, which overcomes the disadvantages associated with the prior art structure described above. This object is achieved by a surge arrester according to the invention. In the surge arrester according to the invention, both the working part and the supporting part are exposed to the environment around the surge arrester and each forms an appropriate length of creep distance between the end fittings. It is shaped to be.

Eliminates the outer porcelain housing by using insulating pull rods to mechanically hold the surge arrester together and by forming the working elements of the pull rod and surge arrester to provide sufficient creep distance can do.

Thus, according to one aspect of the invention, the rod is at least 30 times smaller than the corresponding round cylindrical rod with a smooth creepage between the end fittings of the surge arrester.
% Threads are formed. According to another aspect, the rod comprises a flat, creepage-enhancing shrink mounting casing in the form of a grooved shrinkable hose. As a result, the following advantages (in comparison to surge arresters with a porcelain housing) are obtained, in particular:

a) There is no gas space enclosed in the surge arrester. As a result, there is no danger of explosion in the event of an accident inside the surge arrester and pressure build-up. Therefore, the components of the surge arrester do not come off and no secondary disaster occurs.

b) In principle, it is not limited by the space in the porcelain housing, so at relatively low cost an unspecified number of parallel legs (stacks of surge arrester elements) can be used to reduce this surge. An arrester can be configured.

c) This surge arrester is generally shorter than a surge arrester with a porcelain housing. Surge arresters using porcelain housings are bulky due to the need for large end fittings.

d) The weight of the surge arrester is reduced.

e) The cooling effect of the working part of the surge arrester is improved.

The required creep distance for the active part of the surge arrester can be obtained in several different ways.

For example, the envelope surface of the surge arrester element can be tightly surrounded by an overlapping protective ring and guide ring. These rings are formed from a material that is resistant to creep current.

Alternatively, the operating element of the surge arrester can be configured as an elongated element having a plurality of annular projections located at a creep distance. The surge arrester elements are stacked one on top of the other in the axial direction. The projections of these surge arrester elements are made of the same material as the other parts of the surge arrester element, and
The other part of the arrester element forms a coherent unit (in principle, as shown in EP-A-0 196370) with the other parts. Advantageously, the envelope surface is provided with a protective coating made of an electrically insulating material.

The active part comprises a tightly surrounding casing made of plastic or rubber material which is resistant to creep currents. The casing is attached with shrinkage treatment and has a groove.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

(Embodiment) The surge arrester shown in FIGS. 1 and 2 has a working portion composed of three parallel legs. This working part is in the form of a stack of cylindrical ZnO varistor blocks 10 (FIG. 3) arranged coaxially. The stack is placed between a bottom plate 4 and a top plate 5 and is mechanically held together by three insulating tensile rods 6, for example made of glass fiber. These tension rods are
They are provided at equal intervals along the periphery of the surge arrester. Instead of using three rods, for example,
A single rod may be located between the three varistor stacks along the longitudinal axis of the surge arrester. The rod 6 has an end nut 7. In order to obtain the required contact pressure during the varistor block, the end upper plate 5 is provided with a spring package 8 around each tension rod 6. Alternatively, these spring packages 8 can be arranged at one end of each varistor stack.

The illustrated surge arrester has a length of, for example, 2 m. Each stack may be composed of, for example, about 70 varistor blocks. To mechanically reinforce the surge arrester, a series of metal support plates 9 are arranged between the stacks and are evenly spaced between the end plates 4,5. These support plates 9 are formed with recesses,
The recess corresponds to the cross section of the varistor block and forms a fixed seat for the adjacent block. Thus, the plate 9 extends across the stack, electrically connecting the stacks in parallel.

FIG. 3 shows how the varistor stack is assembled over the distance between the support plates 9. The end surface of the round cylindrical varistor block 10 is provided with an electrode coating, for example in the form of a copper or aluminum layer deposited by plasma spraying, the varistor blocks of the stack being connected in series. The block also includes an electrically insulating envelope protection means having a structure which is essentially the same as that shown in U.S. Pat. No. 4,352,140.
This envelope protection means may be, for example, a silicone rubber or EPDM tightly surrounding the varistor block.
It comprises a rubber protection ring 11 and another guide ring 12, for example made of polypropylene. By means of these guide rings 12, the varistor blocks can be stacked on one another and the varistor blocks can be restrained laterally. At the same time, the guide ring seals the stack of varistors, so that any ionized gas which may be produced by a glow discharge between two adjacent blocks does not diffuse out. The guide ring 12 has a peripheral fin 13 protruding in the radial direction so that the creep distance can be increased along the stack. The protection ring 11 has an axial length substantially the same as the varistor block and has an outwardly directed peripheral projection 14 for fixing the guide ring 12 in the axial direction.

Further, since the fins 13 are provided on the guide ring 12 with a long creep distance, the mechanical stability of the guide ring 12 is improved. Thereby, the number of metal support plates 9 can be significantly reduced, or these metal support plates can be omitted altogether. The above-mentioned fins or projections, protective seals or coatings may be formed directly on the varistor block.

The rods 6 are arranged to mechanically support the surge arrester, and in order to provide a sufficient creep distance along the rods 6, they may be formed, for example, with grooves or through slots. it can. A flat crimped rod may be used, for example, to shrink a commercially available grooved shrinkable hose to obtain the required creep distance.

The surge arresters shown in the drawings are mainly intended for indoor use and provide overvoltage protection for high voltage equipment installed in a protected environment, for example equipment such as high voltage DC thyristor valves. Can do it.
Also, the structural principle proposed by the present invention can be equally beneficially applied to outdoor surge arresters.

The invention is not limited to the embodiments shown in particular, but can be modified in any way within the scope of the claims.

[Brief description of the drawings]

FIG. 1 is a side view of a surge arrester constructed in accordance with the present invention. FIG. 2 is a cross section of the surge arrester along the line II-II in FIG. FIG. 3 is a longitudinal sectional view of three varistor blocks connected in series. The varistor block has an envelope protection means attached to the surge arrester. 1,2,3… stack of varistor blocks 4… bottom plate 5… top plate 6… tension rod 7… end nut 8… spring package 9… metal support plate 10 varistor block 11… … Protective ring 12 …… Guide ring 13 …… Peripheral fins 14 …… Outward peripheral protrusions

Continuation of the front page (56) References JP-A-56-105603 (JP, A) JP-A-53-104837 (JP, A) JP-A-62-114201 (JP, A) , U) Japanese Utility Model 57-124995 (JP, U) Japanese Utility Model Utility Model 61-156202 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01C 7/02-7/22

Claims (6)

(57) [Claims] 1. A surge arrester for high voltage, comprising a working part and a supporting part, said working part comprising two end fittings (4,5) and a plurality of metal oxide varistor materials. A substantially cylindrical surge arrester block (10), said surge arrester blocks (10) being stacked together and disposed between said end fittings (4,5). (1,2,3), the support portion extending between the end fittings (4,5) to at least one mechanically holding the surge arrester blocks (10) together. A rod of insulating material (6),
Both the working portion and the support portion are exposed to the environment around the surge arrester and each is shaped to provide a long creepage distance between the end fittings (4,5);
The rod (6) is threaded or grooved such that the creepage distance between the end fittings (4,5) is at least 30% longer than the corresponding rod having a smooth, round cylindrical shape. Surge arrester characterized by being done. 2. A surge arrester for high voltage, comprising a working part and a supporting part, said working part comprising two end fittings (4,5) and a plurality of metal oxide varistor materials. A substantially cylindrical surge arrester block (10), said surge arrester blocks (10) being stacked together and disposed between said end fittings (4,5). (1,2,3), the support portion extending between the end fittings (4,5) to at least one mechanically holding the surge arrester blocks (10) together. A rod of insulating material (6),
Both the working portion and the support portion are exposed to the environment around the surge arrester and each is shaped to provide a long creepage distance between the end fittings (4,5);
A surge arrester characterized in that said rod (6) is inserted into a flat-surface, creepage-extending shrink mounting casing in the form of a grooved shrinkable hose. 3. The surge arrester according to claim 1, wherein said surge arrester comprises:
The surface of the stacked body of the block (10) is tightly surrounded by annular protective members (11, 12) made of an insulating material, and the protective members are provided on the surge arrester blocks arranged in a stack. A surge arrester arranged so as to overlap with each other and having at least one annular protrusion (13) formed on the protective member to extend a creepage distance. 4. The surge arrester according to claim 1, wherein said surge arrester comprises:
The block (10) has on its surface a plurality of annular projections formed of a metal oxide varistor material and extending the creepage distance, and these annular projections are arranged on top of each other in the axial direction of the surge arrester block. The surface of the arrester block is also provided with a protective coating of an electrically insulating material, the coating being formed and fixed on the surge arrester block. 5. A surge arrester according to claim 4, wherein said coating comprises a layer of polymer or elastomer or a layer of glass or ceramic material. 6. A surge arrester as claimed in claim 1, wherein said working part has a tightly surrounding casing, said casing being heat-shrinkable. A surge arrester made of a flexible plastic or rubber material, mounted by shrinkage, equipped with grooves and resistant to creep current.